Distributed fiber optic technology reveals hydraulic fracturing processes in a large-scale artificial sand-conglomerate model

Understanding fracture evolution is essential for evaluating hydraulic stimulation performance. Conventional monitoring methods, such as sparse geophone arrays and piezoelectric sensors, often lack sufficient spatial resolution or temporal coverage. In this study, we demonstrate that distributed acoustic sensing (DAS) provides a robust alternative for real-time, full-cycle monitoring of hydraulic fracturing. A large-scale laboratory experiment was conducted on a 2 m × 2 m × 1 m artificial sand-conglomerate block under true triaxial stress. Embedded optical fibers recorded both high-frequency acoustic emission (AE) events and low-frequency strain-rate responses. The high-frequency DAS data captured 1333 AE events correlated with pressure variations, revealing distinct rupture stages and suggesting a fluid-driven fracturing mechanism (b = 1.26). The low-frequency responses resolved evolving three-dimensional strain-rate fields, identifying fracture propagation, polarity reversals, and delayed reactivation. Numerical simulations using a 3D displacement discontinuity method reproduced observed strain features and validated their link to fracture geometry and mechanical slip. These results highlight the potential of DAS to characterize fracture dynamics at high resolution, with implications for stimulation optimization, fracture modeling, and geohazard assessment in complex lithologies.